Quick-acting, amplifying break key for wireless telegraphy



Aug. 26 `1924. 1,506,580 Y, H. E. HALLBORG'ET AL.

-I QUICK ACTING AMPLIFYING BREAK KEY FOR WIRELESS TELEGRAPHY Filed oct'. .25 1920 a sheets-sheet 2 A rra/mers Aug. 26 1924. v 1,506,580

. H. E, HALLBORG ET AL QUICK ACTING AMPLIFYING BREAK KEY FCR WIRELESS TELEGRAPHY Filed oct. 25. .192s a sheets-sheet 5 v j? mailman-` n 96? in@ I y lmllwillsl @mi f 2 A l Il! i@ iii Q2) llIIIUI l Anas/951s Aug. ze. 1924. 1,506,580

H. E. HALLBORG ET AL QUICK, ACTING AMPLIFYING BREAK KEY FCR WIRELESS TELEGRAPHY Filed Oc't. ,25 1920 8 Sheets-Sheet 4 i" INVENTo/rs Arm/mers Aug. 26, i924.I 1,506,580

H. E.. HALLBORG ET AL QUICK ACTING AMPLIFYING BREAK KEY FOR' WIRELESS TELEGRAPHY Filed oct. 25. 1920 a sheets-sheet s A TOBNEYS Aug. 26; 1924. v 1,506,580

i H. E. HALLTBORG ET Al.

lQUICK ACTING AMPLIFYING' BREAK KEY FOR WIRELESS TELEGRAPHY 25. 1920 8 Sheets-Sheet 6lv Filed Oct ATTORNEYS A Aug. 26.51924;r

v H. E. HALLBORG E1' AL. vQUIGKv ACTING -AllPLIFYING BREAK KEY FOR WIRELESS TBLEGRAPHY j' Filed oct. 25. 1920 f a sheets-sheet 7,;

' er mon/lfm;

WITNESSES Patented Au, 26, i924.

vUNlTED STATES rsoassa PATENT OFFICE.

HENRY EMMANUEL HALLBORG, OF NORFOLK, VIRGINIA, AND HAROLD REDMORE MILLER, F WASHINGTON, DISTRICT OF COLUMBIA.

QUICK-ACTING, AMPLIFYING BREAK KEY FOR WIRELESS TELEGRAIHY.

Application filed October 25, 1920.

To all l1li/1.0m 'it may concern.'

Be it known that we, HENRY EMMANUEL HALLBORG, a. citizen of the United States, and residing at Norfolk, in the county of Norfolk and State of Virginial and HAROLD Reunions MILLER, a citizen of the United States, and residing at lVashington, in the District ot Columbia, have invented certain new and useful Improvements in Quick- Acting, amplifying Break Keys for -Wireless Telegraphy, of which the following is a specilication.

Our invention relates to improvements in wireless apparatus, and it consists in the constructions, combinations and mode of operation herein described and claimed.

One of the foremost objects of the inveniion is to provide a device to be used in conjunction with wireless telegraph apparatus, enabling the reception of amplified signals from either a damped or undamped V"are distant transmitter between the dots and dashes of the transmitter of the local station, thereby saving muchtime in the handling of messages and also eliminating the send to receive7 transmitter switch.

si further object of the invention is to provide an improved relay or break key adapted more particularly for handling messages at high speed by wireless telegraph, to this end the break key being provided with an annealed sheet steel magnetic circuit.

A, :Further object oi" the invention is to provide a quick-acting break key which is rendered sensitive to the slightest touch of the hand key by virtue of the selection of magnetic material possessing a maximum permeability at minimum magneto-motive torce, thus obtaining the required rapidity oi response and contact pressure and wholly avoiding' sluggishness of operation.

A further object of the invention is to provide an improved break key wherein all of the parts are easily accessible, this being particularly true of the various contacts which are also independently adjust-- able as to the order of striking.

Other objects and advantages will appear in the following specification, reference being had to the accompanying drawings, in which:

Figure 1 is a front elevation of the improved wireless relay or break key,

Figure 2 is a detail sectional view of the Serial No. 419,231.

front auxiliary contacts which control the shunt condenser of the telephones,

Figure 3 is a plan view of the break illustrated in Figure 1,

Figure 4 is a detail plan view of the main contacter,

Figure 5 is a detail perspective view of the insulating coupling on which the contactor arms of the main contactor are mounted,

Figure 6 is a detail end elevation of the key, showing the main contact pedestals which cooperate with the main contactor,

Figure 7 is a longitudinal section of the break key, taken substantially on the line 7-7 of Figure 3,

Figure 8 is a horizontal section taken substantially on the line 8-8 of Figure 1,

Figure 9 is a detail horizontal section taken substantially on the line 9-9 of F igure 1, showing the lield coil connection posts,

Figure 10 is a detail side elevation oi' a part of one of the lield coils and one ot the libre washers,

Figure 11 is a detail cross section of one or" the contact pedestals, taken substantially on the line 11--11 of Figure 3,

Figure 12 is a detail section of the on the line 1212 oi Figure 11,

Figure 13 is a detail plan view of a part oi' the upper casing and the base,

Figure 14 is a detail cross section on the line 14 14 of Figure 7, showing the mor-- able stop of the armature shaft, with its auXili ary contact arms,

Figure 15 is a detail plan view oi the upper bearing of the armature shaft,

Figure 1G is a view of one of the auxiliary Contact arms in Figure 14, the various parts being disassembled,

Figure 17 is a longitudinal section o1c the break key, illustrating the associated parts of the arma-ture shaft in detail,

Figure 18 is a diagram illustrating the application of the quick-acting break key to a spark system having vacuum tube and ampliiier system of reception,

Figure 19 is a diagram illustrating the application of the break key to an undamped system having vacuum tube and amplifier system of reception,

Figure 2O is a diagram illustrating the application of the break key to an undamped system using the ignition type of arc transkey pedestal Cil mitter with vacuum tube and amplifier system of reception, and

Fignre21 is a diagram illustrating the application of the break key to a 500 cycle vacuum tube transmitter with vacuum tube and amplifier system of reception.

A brief survey of the particular' field in which the improved relay or break key is employed, will aid in the understanding of the purpose of the invention. The break key is primarily designed to enable speeding up of radio traliic between ships at sea and ship and shore stations. Such speeding up, when the instruments are operated manually, is largely dependent upon the development of a simple, fast and dependable break key. The merits of the break system have long been recognized, yet out of a wide experience it has been found that none of the break keys in present use have been unqualified successes with contact detectors, and particularly have none been successful with vacuum tube detector and amplifier receptions.

The major defects of break keys in common use have been observed to be as follows:

(a) Sluggishness of operation.

(Z2) Noisy reception.

.(0) Rugged contact detector required.

(CZ) Inaccessibility and unreliability of adjustment.

(e) Frailness of construction.

( Multiplicity of contacts.

As more fully appears below, the above defects have been satisfactorily remedied `in the herein disclosed break key. By using a magnetic material having veryhigh permeability at low magnetizing force, a high magnetic flux density is instantly developed, giving the proper contact pressure which is necessary for high speed work. Cast and wrought iron have been found entirely useless for high speed work. Cast steel is satisfactory for comparatively slow speeds, as for example, 60 w. p. m. For Ihigh speed work, as for example 150 w. p. m. and over, the use of annealed sheet steel has been found absolutely essential. This -material is employed in the magnetic circuit ofthe improved key.

There is a very close relationship between the magnet materials employed in the break key. and the speed at which the key can be operated. By using a magnetizing current of proper strength, a very high magneto-motive force is instantly developed giving the proper contact pressure which is necessary for high speed work. To this end, the break key is sensitive to the slightest touch of the hand key so that the sluggishness of operation, enumerated above, is wholly avoided. The reader may now follow the construction of the break key, the major parts being described in order. f

The base comprises the' lower and upper casings 1 and 2; .the former with feet 3, by means of which the key is iixed in place, and a bridge l with a central bore 5 for the reception of the flanged brass bearing bushing 6.

Companion flanges 7 and 8, respectively on the lower and upper casings, have oppositely extending lugs 9 and 1,0 through which the screws 11 pass to clamp the laminated magnet frame l2 in position when the partsare assembled.

The magnet frame includes the cally opposite pole pieces 13 and 14, well illustrated in Figure 8, on which the field coils 15 and 16 are mounted. The laminations of the magnet frame 12 are made of annealed sheet steel, and when the field coils 15 and 16 are properly energized, a powerful magnetomotive force is set up at the pole pieces for theattraction of the adjacent ends of the laminated varmature 17, substantially in the center of the shaft 18. As well shown in Figures 7 and 17, this shaft is made in two parts: Both parts have brackets 19 and 20 with lugs similar to the lugs 9 and 10 of the base casings, for embracing the laminat-ions of the armature 17 and holding them as a unit when the Arivets 21 are driven home.

Both shaft ends have collars 22 and 23, respectively bearing on the bushing 6 at the bottom` and engaging the bearing 24 at the top. This bearing is made in two parts, as in Figure 15, for convenience in assembling around the shaft. j

A movable stop 25, riveted to the upper shaft at 2G, limits the counter rotation of the shaft by virtue of the spring 27, when the coils 15 and 16 are deenergized and the armature 17 is released. The rotation of the shaft, under the influence of the magnets, is limited by the engagement of the stop 25 with the fixed stop screw 2S, which may be adjusted, however, and fixed to its adjustments by the jamb nut 29. Surmounting the upper' shaft 18 is the main contacter which carries the contacts A and B, generally so indicated for the purposes of the description below. The upper shaft also carries brass contact arms 3() and 31, at right angles to the spring steel contact arms 32 and 33 which carry part of the main contacts A and B, for the purpose of controlling the auxiliary contacts c and l). The arrangement ofthe auxiliary contact a is precisely the saine as b when the break key is employed in the spark system shown diagrammatically in Figure 18, and therefore a brief description of the first will suiiice for the second.

As shown in Figure 2, the auxiliary contact a comprises the'contact bracket 84 and bearing bracket 35, both securely mounted on the insulating base 36 by means of machine screws 37, `which base is in turn diametrif mounted on the projection 38 from the upper casing 2, by means of screws 39. The contact arm 40 is movable on its fulcrum 41 on the base of the bracket 35, being urged toward the bracket 34 by the spring 42 and away from the bracket by the contact arm 30. The bond Wire 43 provides a good electrical connection between the bracket and contact arm 40, which connection might be interfered With Were the metallic path through the fulcrum 41 relied upon solely.

The arm carries a silver contact tip 44, to engage a similar tip 45 in the brass contact stud 46 orv the contact bracket The stud 46 is adjustable and its adjustments are set by the jamb nut 47. A brief description of the details of the main contacts A and B Will enable the reader to pass on to the diagrams in Figures 18, 19, 20 land 21, in Which connection the operation of the break key is described.

Consider first the main contact A: The arm 32 of the main contacter, carries contact tips 48 and 49, joined by a copper connector 50, for engaging companion contact tips 51 and 52 on the studs 53 and 54 of the pedestal 55. The contact studs are screwed into contact holders 56 and`57 of the pedestal 55, Where they are held in place by jamb nuts 58. insulating Washers 59 and bushings 60 separate the Contact holders 56 and 57, the central screw 61 securing all of the parts on the contact pedestal to the upper casing 2. Dovvel pins 62 prevent relative turning of the Washers and bushings.

The elements of the main contact B are precisely like those of the contact A but :tor purposes of distinction are designated as follows: rThe arm 33 of the main contactor has contact tips 63 and 64, joined by a copper connector 65, andceoperating With contact studs 66 and 67 of the other pedestal 68. These studs are made of hard ground ccpper and have no.` extra contact tip, Whereas the studs 53 and 54 and the pedestal 55 are made of brass and have extra contact tips 51 and 52, made of silver.

Similarly, the tips 48 and 49 are made of silver, Whereas the tips 63 and 64 are of copper. Bushings 69 and 70 separate the Contact holders 71 and 72, as in the first instance, the Washers 73 .insulating` the lowermost holder from the upper casing 2. The contact holders 56, 57, 71 and 72 respectively carry binding screws 74, 75, 76 and 77, so that the necessary circuit connection shown in the .diagram in Figure 18, may be made. The 'shunt condenser 78 of the telephones 79, although shown separated from the break key, is housed Within the base of the break ke j, in actual practice, and to thatk end, the base is provided at one end With a pair of connection posts 80, 81, similar te the connection posts 82, 83 of the lield coils l5 and 16, so that the Wires 84, 85 may be connected between the break key and the telephone sets.

Generally described, the spark system in Figure 18 comprises the spark transmitter 86, the generator 87, the receiver 88, the vacuum tube detect-or 89, the iirst and second stage audion amplifiers 90 and 91 and the iilament ballast resistance 92. The gener'- ator 87 is a 500 cycle generator, and its line Wires 93, 94 are connected to the binding posts 76 and 77 of the contact pedestal 78, the current thus reaching the contact tips 66 and 67. Although not so shown, it is to be noted that the device is operative on more than the two stages of amplification described.

Wires 95, 96, lead from the tips 44, 45 of the auxiliary contact respectively to the battery 97 and movable member 98 of the rheostat 99, which serves the purpose of bringing the filament F of the audion detector 89 to the proper degree of incandescence, and directly to the lilament F (in the case of the Wire 96).

The filament ballast resistance 92 is connected in parallel with the Wires 95, 96. `Wires 100, 101 shut the prima-ry oi the receiving set 88 when the tips 51, 52 of the main contact A are bridged.

The operation of the arrangement in Figure 18 is best understood from the following schedule:

ance 92 in ilament circuits of ance 92.

vacuum tubes E9, 90 and 91.

lt is to be understood that the insertion cf the variable ballast resistance 92 is of considerable importance especially When used on very high power sets, This resistance operates to reduce the emission of ions in the thermionic current in the sending position of the key. At such a time (especially in a high-powered transmission set) there is grave danger of injury to the vacuum tube by induced current during the sending operation, During such sending operation the current inducedthereby, increases the therniionic current (which is the current iiowing from the filament to the plate) tending to the detriment of the vacuum tube, but it is here that the resistance 92 performs its functions. T his function is to reduce the emission of ions from the filament to such an extent that the thermionic current never exceeds a safe value when the induced (sending) current is added lli thereto. The shunt condenser 78 of the telephones 79 is a very important fea-ture. Ordinarily, the elimination of noise in the telephones is a particularly difficult problem in the case ot highly amplified received signais, this being so because the plate circuit of the amplifier is extremely sensitive to any change in its constants and particularly to a change in its resistance.

The paralleling of the telephones 79 by the condenser 78 does not aiiect the resistan-ce of the plate circuit and hence arc or spark signals are readily received, all noise in the telephones, as caused by induction in the local transmitter, being prevented f by the condenser.

This principle of the invention is operative with any type of transmissionv apparatus and with any kind of detector (crystal, vacuum tube). Thebattery 91a produces a steady iioW of current from the iilament to the plate of the detector 91, and so long as it remains at its normal value no sound in the telephones results. When transmitting signals, the signal pulse which is superimposed on the plate current, produces a current of such strength that a deafening sound results in the telephones. However, by providing thecondenser v78, the signal pulse is shunted around the telephones rendering them insensitive to eX- citation Jfrom the loc-al transmitter.

The degree to which the signal pulse is shunted from the telephones depends on the relative reactances of the telephones land condenser, and the degree of reactance ot the condenser depends on its capacity.

Those parts of the Wireless sets in Figures and 20, corresponding to similar parts in Figure 18, are designated by similar reference characters with the exception of the addition of indeX letters e and Z) in the respective diagrams. For example, in Figure 19, the transmitter is designated 86, the high frequency generator 87, the receiver 88a, etc., While in Figure 20, the transmitter is indicated 86", the arc set 87h, the receiver 88h, etc. The operation of the break key in Figure 19 can be understood at a glance from, the following schedule:

UNnAMrnn VVAvE SYSTEM.

Hilf/lt flingue/)icy generator transmitter.

ggg. Sending position Receiving position.

AU.. Connects high frequency gen- Disconnectshigh frequency erator 87e' to antenna system generator 87u. 86H.

B Disconnects receiver 88e from Connects receiver S8 to antenna system. antenna system.

a. Connects condenser of low re- Disconneets 'condenser 78e.

aetance 78A in shunt to telephones 79H.

b Short circuits resistance in field Inserts, resistance in cld of highfrequency generator. of thigh frequency genera or.

Lacasse r[he operation `of the` break key in its position in the arrangement 1n Figure 20, is. also best understood from the accompa-nying schedule: UNnAMrnD WAVE SYSTEM.

tenna system. from antenna system.

B,..- Diseonnects receiver from an- Connects receiver to antenne system. tenna system. 11....- Connects condenser of 10W re- Disconnects condcnserirom actance in shunt to telephones. telephones.v b. Closes magnet circuit of igni- Opens magnet circuit ofv y tion key. ignition key.

The reader must understanchin connection with the three diagrams described above, that in each instance the ordinary hand key 102 is used to energize the field coils and 16 from any suitable source of electrical energy. This key is employed by the operator in sending his messages, a depression of the key energizing the coils of the relay of break-key, a release thereof deenergizing them. The attraction of the armature 17, by the energization of these coils, rotates the shaft 18 and consequently 'closes and opens certain ot the contacts as clearly pointedy out in the above schedules in connection with the various Wireless systems. from the above schedules, that 'when the break key is in one positionthe contacts A, B, a, Z), enable the receiving of a signal, WhileJ when the same contacts are in the opposite positions they enable the sending of a signal. lt is by this dual performance of the break key that Wireless traiiic is successfully speeded up and many actual exhaustive tests have demonstrated the merits of the improved break key. The foregoing description is purposely made as brief as possible so as not to seriously interfere with a quick understanding of the operation of the break key, attention being now directed to those details of construct-ion Which are omitted above but must now be included. Beginning wth the contact arm (and the same construction is carried out in respect to the arm 31) the free end is reduced into a spindle 103, on which insulating Washers 104 are iitted, the insulating sleeve 105 fixing' the space betweenthem The metal sleeve 106, mounted on the insulating sleeve `105 between the Washers 104, engages the contact arm 410 of the auxiliary contact a (also ZJ), a brass collar 107 being pinned to the spindle 103 to hold the various parts in Figure 16 in place.

The movable stop 25 is substantially of the shape shown in Figure ll-,including a receptacle 108 in which the circular plug The reader Will also understand f oi the coupling 109 is iixed by the rivets 26. A metallic bracket 110 is secured to the coupling 109 at each side` and in abutment with dividing ribs 111, for the purpose otl providing mountings for the arms 32, 33 ot the main contactor. rlhese arms are held in place by clips 112 and suitable screws, all as clearly shown in Figure. 4. The coupling 109 is made ot' insulating material as illustrated.

rihe laminations ot the magnet frame 12 are punched out of a single sheet of annealed steel in the shape shown in Figure 8, heated rivets 113 being placed at the important points to hold the laminations together. The heads of the. outermost ones of the rivets are pocketed in recesses 114 when the upper and lower casings of the base are assembled, so as to constitute keys as it were, to assist in the assembling.

To further this end, the frame holding lugs 10 are flat faced on the inside, these lugs, together with the rivets just mentioned above7 securely holding the. magnet traine in its proper place.

Mention has been made of the adjustability oi'L the various main and auxiliary contacts A, B, a., o, but the particular construction in connection with which such mention has been made, must be supplemented by data giving the best contact adjustments, determined by actual practice. tiuch has been found as follows:

Contact A: A very small opening o1 about l/100 inch. lVhen the key is in the open position this opening acts as a receiver safety gap.

Contact B: Gpeningl of about 1/16 of an inch.

Contact a: `Opening of about 1/200 of an inch.

Contact Y): Opening of about 1/200 of an inch.

.From the foregoing gap spacing, the reader will understand at once that all contacts do not engage simultaneously, the order o1 closing and opening varying in the three systems in diagrammatic Figures 1S, 19 and 20. For the spark system in Figure 18, the order o'l closing is A-B, and order of opening is B-Act For the undamped system in Figure 19, the order of closing is a-ZJ-A, and order oft opening` is A-b-a; and for the undamped system in Figure 20, the order of closing is A- and order oit' opening is b-A-c- B opens immediately after a closes, B closes immediately after A opens.

Further experiments have developed the transmitting circuit illustrated in Figure 21 and is so directly applicable to the improved relay or break key that mention or" the arrangement must be made. 87C is a 500 cycle generato-r, as in the preceding diagram, which supplies energy to the primary winding 115 of the power transformer 116.

This transformer supplies current at high voltage to the circuit 11T of the plates 118 of the vacuum tubes 119 and to the primary Sending position. Receiving position.

A Connects generator 87C to pri- Disconnects generator 87e,

mary 115 of transformer 11G to plate circuit 117 and antenna system.

etc., from antenna systern.

B Shunts primary of receiver cir- Removes shunt of primary cuit 123 from antenna system. 1:23 from antenna system.

a Connects condenser of low re- Disconnects con d c n ser actance 124 in shunt to telefrom telephones. phones 125.

b Inserts resistance 126 in trans- Removes resistance from former circuit 127 to reduce filament condenser' cirincandescence of filaments cuit to increase incan- 128. dcscence of filaments.

For the vacuum tube transmitter system in Figure 21, the order of closing is (t-l-- -A, order ot opening is A*'-B-a.

Vfhile the construction and arrangement of the improved wireless break key as herein described and claimed is that of a generally preferred form, obviously modifications and changes may be made .vithout departing from the spirit oi the invention or the scope of the claims.

lVe claim 1. Wireless telegraph transmitting and receiving apparatus, comprising a series of oscillation valves7 telephones in operative connection with said valves for receiving highly amplilied signals, and a condenser in shunt with the telephones for shunting the signal pulses of the transmitting apparatus around the telephones thereby preventing noise therein.

2. Wireless telegraph apparatus, comprising a series of oscillation valves, telephones in operative connection therewith, a relay or break key with contacts placing the oscillation valves in a signal-receptive connection when the key is in one position, and a condenser normallv shunted across the telephones when the key is in the original position, disconnected from the telephones when the key is in the signal-receptive position.

3. -Radio telegraph apparatus comprising the combination of a receiver having a detector, an associated circuit including` a source of current, telephones situated in said circuit; a transmitter, a sending key embodied in said transmitter, and a condenser infsaid circuit in shunt with the telephones adapted to render the telephones insensitive to excitation of said circuit upon operation of said key.

t. Radio' telegraph apparatus comprising the combination of a receiver having a vacuum detector, an associated circuit including a source of current, telephones situated in said circuit; a transmitter, a sending key embodied in said transmitter, and a condenser in said circuit in shunt with the telephones adapted to render the telephones insensitive to excitation of said circuit upon operation of said key.

Radio telegraph apparatus comprising a transmitter and receiver, a circuit embracing a detector, associated amplifying means and telephones situated in said circuit, a telegraph key in said transmitter, and a condenser in said circuit in shunt with said telephones for the purpose of rendering; them insensitive to excitation from the local transmitter during` transmitting periods.

(3. Radio telegraph apparatus comprising a receiver and local transmitter, a circuit in said receiver embodyingl a detector, associated amplifying means including.;` telephones, a key in said transmitter, and a condenser of loiv reactance in respect to the telephone reactance at signal pulse frequency situated in said circuit but in shunt across the telephones for the purpose of rendering` the telephones insensitive to excitation from the local transmitter upon operation of said key.

7. Radio telegraph apparatus comprising the combination of a vacuum tube detector with an associated circuit embracing telephones and a source of current, a condenser bridging the telephones, and a break key having a closed and open position, and a condenser shunting the telephones when the key is closed to prevent disturbance of the steady thermionie current, but when open, to cut/out the condenser so that an incoming signal pulse may be imposed on said current and result in a response by the telephones.

8. Radio telegraph apparatus iiicluding` telephones, a condenser adapted to be shunted around the telephones, a receiving set, a

transmitter, and a break-key adapted to first shunt the condenser across the telephones, short circuit the primary of the receiving` set, and energize the transmitter in moving to the sending position7 and performing the same functions in reverse order in moving to the receiving position. Y

9. In wireless telegraph apparatus con-- sisting of a series of oscillation valves in which a steady thermionic current and audio frequency currentexistand telephones in circuit with said valves, the method of removing from the telephones the audio fre-- quency current Without disturbance to the normal steady thermionic current.

10. In Wireless telegraph" apparatus consisting of a series of oscillation valves in which a steady thermionc current and-audio frequency current exist, and signal responsive means in circuit with said valves, the method of removing from said signal responsive means the audio frequency current Without disturbance to the normal steady thermionie current.

1l. In Wireless telegraph apparatus consisting of an oscillation valve, means for maintaining a steady thermionic current therein, an outgoing signal pulse superimposed upon said thermionic current, and telephones in circuit with said valve, the method of shunting said superimposed current around the telephones to prevent objectionable noise therein and Without disturbing said thermionic current.

12. lVireless telegraph apparatus comprising a series of oscillation valves, telephones in operative connection with said valves for receiving amplified signals, a break key with contactsplacing the oscillation valves in a signal-receptive connection when the key is in one position, and a loW-reactance condenser normally shunted across the telephones When the key is in the other position, but disconnected from theA telephones When the key is in the signal-receptive thereby making the telephones instantly responsive when the key is released.

HENRY EMMANUEL l-ILLBORG. HAROLD REDMORE MLLER.

position, 

